This invention relates to high temperature metal continuous casting machines, and more particularly, to an improved mold cooling system for continuous casting machines.
In conventional continuous casting machines, molten metal is passed through an open ended flow through mold which may be curved or straight. The mold may be oriented vertically or horizontally and is generally square or rectangular in shape but may be of various geometrical configurations.
The mold which forms the metal strand confines the liquid metal and provides for its initial solidification, or formation of the encasing shell. The solidifying strand is extracted continuously from the bottom or exit end of the mold at a rate equal to that of the incoming liquid metal at the top or entrance end, the production rate being determined by the time required for the outer shell to harden sufficiently so as to contain the inner liquious core by the time the strand exits the confines of the mold.
In one prior art method of cooling the liquid metal in continuous casting machines, a water system recirculates cooling water around the outside of the mold cavity liner. The water enters into the bottom of a pressure tight vessel in which the mold cavity liners are contained and flows upward along the outer surface (or cold face) of the mold cavity liner in a direction opposite from that of the moving liquid metal. This counter-current water flow has been accepted as the most efficient for heat transfer in continuous casting machines. Because the cooling water is under high pressure and flows at a high velocity an enclosed pressure vessel must be utilized. A sealed cooling system is provided by fixing the mold cavity liners to the pressure tight vessel at both ends.
It is essential that sufficient heat be extracted from the liquid metal through the mold cavity liner by the cooling water to not only produce the required strand shell formation but also to prevent the mold cavity liner from melting. Contact between the liquid metal and the mold cooling water may result in a steam generated explosion.
As heat transfers from the liquid steel to the circulating cooling water, through the walls of the mold cavity liners, some of the water evaporates resulting in the creation of a steam barrier on the surface of the mold liner which tends to reduce, and limit, heat transfer. Also, because there is no adjustable control of the water flow rate as it passes over the outside (or cold) surface of the mold cavity liners, there is a tendency for the solidified shell of the cast strand to contract as it cools thereby resulting in the formation of gaps between the newly formed solidified skin and the mold cavity liners. These gaps also result in a reduction of heat transfer and cause reheating of the solidified shell. A combination of this reheating effect and the ferrostatic pressure will subsequently cause the solidified shell to expand and contract the mold cavity liner again. This process of contraction and expansion will be repeated continually as the strands pass through the confines of the mold cavity liner.
One type of prior art continuous casting machine cooling system such as that shown in U.S. Pat. No. 3,759,309, attempts to control the solidification rate within the mold by spraying steam heated water at a controlled temperature against the outer surface of the mold.
In another type of prior art device disclosed in U.S. Pat. No. 3,049,769, mold cooling was achieved by providing individual flow passages along the mold surface. While this did provide some limited control circumferentially, there was no control longitudinally along the mold surface. In addition, prior art mold cooling systems which include this type of integral cooling jacket required substantially larger and more complicated mold oscillation systems in order to oscillate both the mold and the relatively heavy cooling system components.